Regioselective Reaction of 2-Indolylmethanols with Enamides

A highly regioselective reaction of 2-indolylmethanols with enamides has been developed at room temperature by using AlCl₃ as a catalyst. A wide range of hybrids (40 examples) of indoles and enamides were obtained in moderate to good yields (up to 98% yield). This transformation represents the efficient way to introduce biologically important indoles and enamides skeleton into structurally complex hybrids.

Organocatalytic Atroposelective Synthesis of Indole Derivatives Bearing Axial Chirality: Strategies and Applications

Catalytic atroposelective syntheses of axially chiral compounds have stimulated extensive interest in multiple communities, such as synthetic chemistry, biochemistry, and materials science, because of the intriguing characteristics of atropisomerism. In particular, atropisomeric indole derivatives, which contain a kind of five-membered heterocyclic framework, are widely distributed in a number of natural alkaloids, biologically relevant compounds, chiral ligands, and chiral organocatalysts. Hence, the catalytic atroposelective synthesis of indole derivatives bearing axial chirality is of considerable importance and has become an emerging focus of research. However, there are substantial challenges associated with the atroposelective synthesis of indole derivatives, including remote ortho-substituents around the chiral axis, a lower barrier for rotation, and a weaker configurational stability than that of atropisomeric six-membered biaryls. Therefore, the development of effective strategies toward the catalytic atroposelective synthesis of indole derivatives has become an urgent task.In order to tackle these challenges and to accomplish the task, our group devised a unique strategy of designing indole-derived platform molecules and developing organocatalytic enantioselective transformations of such platform molecules to synthesize atropisomeric indole derivatives; asymmetric organocatalysis has tremendous advantages and was the research area recognized by the Nobel Prize in Chemistry in 2021. This Account summarizes our endeavors in the organocatalytic atroposelective synthesis of indole derivatives bearing axial chirality. In brief, we devised and developed a series of indole-derived platform molecules, such as indolylmethanols, (hetero)aryl indoles, oxindole-based styrenes, N-aminoindoles, and indole-based homophthalic anhydrides, by introducing different functional groups onto the indole ring to achieve new reactivity and modulate the reactive site of the indole ring. As a result, these indole-derived platform molecules possess versatile and unique reactivity and are capable of undergoing a variety of organocatalytic enantioselective transformations for preparing structurally diversified indole derivatives with axial chirality.We used these strategies to accomplish the atroposelective synthesis of plenty of indole derivatives with axial chirality, including (hetero)aryl indoles, alkene-indoles, oxindole-based styrenes, N-pyrrolylindoles, and isochromenone-indoles. In addition, we gave a thorough and detailed understanding of the designed reaction by investigating the reaction pathway and activation mode. More importantly, we studied the biological activity of some products and performed catalyst design on the basis of atropisomeric indole moieties, which are helpful for disclosing more applications of indole derivatives bearing axial chirality.In the future, the organocatalytic atroposelective synthesis of indole derivatives bearing axial chirality will indubitably remain a frontier topic in the research area of asymmetric catalysis and chiral indole chemistry despite challenging issues, for instance, the atroposelective synthesis of novel indole derivatives bearing an unconventional chiral axis, the development of atropisomeric indole derivatives into powerful catalysts or ligands, and the discovery of atroposelective indole derivatives as potent drug candidates. We hope our efforts summarized in this Account will encourage chemists worldwide to devise innovative strategies toward solving the challenging issues that remain in this field, thus promoting its development to a higher level.

Diversity synthesis of indole derivatives via catalyst control cyclization reaction of 2-indolylmethanols and azonaphthalene

A series of indole-fused scaffolds and derivatives was synthesized via the cyclization reaction of 2-indolylmethanols with azonaphthalene. These reactions were realized under mild reaction conditions through catalyst control, providing structurally diverse indole derivatives with moderate to excellent yields. This protocol also shows good substrate adaptability, especially in six-membered ring products.

Hypoiodite-Catalyzed Oxidative Umpolung of Indoles for Enantioselective Dearomatization

Here we report the oxidative umpolung of 2,3-disubstituted indoles toward enantioselective dearomative aza-spirocyclization to give the corresponding spiroindolenines using chiral quaternary ammonium hypoiodite catalysis. Mechanistic studies revealed the umpolung reactivity of C3 of indoles by iodination of the indole nitrogen atom. Moreover, the introduction of pyrazole as an electron-withdrawing auxiliary group at C2 suppressed a competitive dissociative racemic pathway, and enantioselective spirocyclization proceeded to give not only spiropyrrolidines but also four-membered spiroazetidines that are otherwise difficult to access.

Synthesis of C3-functionalized indole derivatives via Brønsted acid-catalyzed regioselective arylation of 2-indolylmethanols with guaiazulene

The first Brønsted acid catalyzed method for the construction of guaiazulenyl C3-functionalized indole derivatives was established. The reactions proceeded smoothly at ambient temperature by used (±)-10-camphorsulfonic acid (CSA) as catalyst,...

2-Indolymethanols as 4-atom-synthons in oxa-Michael reaction cascade: access to tetracyclic indoles

The first Brønsted acid-catalyzed oxa-Michael reaction cascade of 2-indolylmethanols with trione alkenes was accomplished. By using this practical approach, a variety of tetracyclic indoles were readily created in an ordered sequence with excellent regio- and diastereoselectivity. 2-Indolylmethanols commendably served as four-atom synthons, as opposed to the common three-atom synthons in the previous literature reports. The regioselectivity issue was well handled by the employment of a strong Brønsted acid catalyst. In addition, its dual role in activation of substrates via hydrogen-bonding interaction and acceleration of subsequent intramolecular cyclization and dehydration was proposed to account for the high reaction efficiency.

Organocatalytic Asymmetric Synthesis of Indole-Based Chiral Heterocycles: Strategies, Reactions, and Outreach

Indole-based chiral heterocycles constitute a class of important heterocyclic compounds that are found in numerous pharmaceuticals, functional materials, and chiral catalysts or ligands. Catalytic asymmetric synthesis, for which the 2001 Nobel Prize in Chemistry was awarded, has been demonstrated to be the most efficient method for accessing chiral compounds. Therefore, the catalytic asymmetric synthesis of indole-based chiral heterocycles has attracted great interest from the scientific community. However, the strategies toward this goal are rather limited, and great challenges remain in this field, such as metal contamination in the products, the limited number of platform molecules with versatile reactivity, and the limited number of catalytic asymmetric reactions that offer high step economy, atom economy, and excellent enantiocontrol. Therefore, novel strategies for the catalytic asymmetric synthesis of indole-based chiral heterocycles are urgently needed. To achieve this goal, our group has developed a series of unique strategies, such as designing and developing versatile platform molecules and their corresponding organocatalytic asymmetric reactions to access indole-based chiral heterocycles. In this Account, we describe our efforts to address the remaining challenges in this research field. Namely, we have designed and developed vinylindoles, indolylmethanols, arylindoles and indole derivatives as versatile platform molecules for the construction of indole-based chiral heterocyclic scaffolds with structural diversity and complexity. Based on the reactivities of these platform molecules, we have designed and accomplished a series of organocatalytic asymmetric cycloaddition, cyclization, addition and dearomatization reactions with a high step economy, atom economy and excellent enantiocontrol. Using these strategies, a wide range of indole-based chiral heterocycles, including five-membered to seven-membered heterocycles, axially chiral heterocycles and tetrasubstituted heterocycles, have been synthesized with high efficiency and excellent enantioselectivity. In addition, we have investigated the properties of some indole-based chiral heterocycles, including their bioactivities and catalytic activities, and showed that these chiral heterocycles have potent anticancer activities and promising catalytic activities in asymmetric catalysis. These results help elucidate the potential applications of indole-based chiral heterocycles in drug development and chiral catalysts. The organocatalytic asymmetric synthesis of indole-based chiral heterocycles has undoubtedly become and will continue to be a hot topic in the field of asymmetric catalysis and synthesis. Our efforts, summarized in this Account, will not only open a window for the future development of innovative strategies toward organocatalytic asymmetric synthesis of indole-based chiral heterocycles but also inspire chemists worldwide to confront the remaining challenges in this field and prompt further advances.

Progresses in organocatalytic asymmetric dearomatization reactions of indole derivatives

This review summarizes the progresses in organocatalytic asymmetric dearomatization reactions of indole derivatives and their applications in total synthesis of natural products, and gives some insights into challenging issues in this research field.

Lewis Acid-Controlled Regioselective Phosphorylation of 2-Indolylmethanols with Diarylphosphine Oxides: Synthesis of Highly Substituted Indoles

The Lewis acid-promoted phosphorylation of 2-indolylmethanols with diarylphosphine oxides is described. The regioselectivity of the reaction can be modulated by the choice of rare earth metal Lewis acid, offering a highly selective approach to structurally diverse indole derivatives in up to 97% yield for over 50 examples. This strategy features high selectivity, good functional group tolerance, and easy scalability. The utility of this method is further highlighted by facile modification of the products to access novel indole-based phosphine ligand.

Direct C3-arylations of 2-indolylmethanols with tryptamines and tryptophols via an umpolung strategy

A Brønsted acid-catalyzed direct C3-arylation of 2-indolylmethanols with tryptamines and tryptophols has been established, leading to a series of potentially bioactive 2,3′-biindole derivatives with a broad substrate scope and generally good yields (38 examples, up to 96% yield).

Brønsted acid-catalysed regiodivergent phosphorylation of 2-indolylmethanols to synthesize benzylic site or C3-phosphorylated indole derivatives

A Brønsted acid catalyzed highly regiodivergent phosphorylation of 2-indolylmethanols with diarylphosphine oxides has been established, which provides an efficient protocol for accessing benzylic site or C3-phosphorylated indole derivatives with structural diversity.